While most of the attention Saturday night at the Freeman Coliseum in San Antonio will focus on whether lightweight world titleholder Mikey Garcia can defeat junior welterweight titlist Sergey Lipinets to win a belt in his fourth weight division, there is another important though lower-profile fight in the weight class in the co-feature.

Rances Barthelemy and Kiryl Relikh will battle for a vacant 140-pound world title on the undercard (Showtime, 10:15 p.m. ET/PT) with the winner not only claiming a belt but also setting himself up for a possible big-money unification fight with Garcia (37-0, 30 KOs) should he defeat Lipinets (13-0, 10 KOs).

Rances Barthelemy vs. Kiryl Relikh

The fight is a rematch of a thrilling encounter from May 20, when Barthelemy and Relikh met at the MGM National Harbor in Oxon Hill, Maryland, on another Showtime undercard. Barthelemy won a disputed decision in a world title eliminator. The result of the fight, in which both boxers suffered knockdowns, was controversial enough -- with many believing Relikh had done more than enough to win -- that a rematch was ordered.

"We look at our co-feature of Barthelemy and Relikh, a controversial fight in 2017, and each of them wasted no time wanting to get into a rematch," Showtime Sports president Stephen Espinoza said.

And so they will go at it once again with Barthelemy believing he did not show his best in the first encounter.

"It's in my character to take this rematch immediately," Barthelemy said. "I was very happy once I found out everything was ready to go for it. I want to prove to the fans and to myself that I can do much better than I did in May. I want to show Relikh how much better I am than him."

"I'm going to change a lot heading into the rematch. Last May I wasn't myself. I didn't feel like I had my legs coming into the fight and I wasn't able to perform how I usually do. This time my conditioning and nutrition is much improved. I'm going to use my legs and use my jab and put on a boxing clinic."

Rances Barthelemy

The fight had originally been scheduled for Feb. 10 but was postponed when Lipinets suffered a minor hand injury that caused the card to be delayed by a month.

Not only does Barthelemy (26-0, 13 KOs), 31, a Cuban defector fighting out of Las Vegas, want to look better in the rematch, he also has a chance to make history. He has already won world titles at junior lightweight and lightweight. A victory would make him the first Cuban fighter to win titles in three weight classes.

"It's on my mind all the time that I have a chance to make history for Cuban boxing," Barthelemy said. "There have been so many great Cuban fighters throughout the years. I never imagined I'd be in position to make history myself but I know it's a reward for my hard work and dedication."

Should Barthelemy accomplish his goal of picking up that third title, he has designs on a fight with Garcia, the big favorite to beat Lipinets, who will be making his first defense.

"This is my second time fighting for a world title and it will be a second lesson for me. This is my time to become champion. I need to do much more during this fight. I have to be aggressive right from the start. I'm sure that I need a knockout to get the victory. He can try to run, but he won't be able to hide from me."

Kiryl Relikh

"A fight with Mikey Garcia is something I want," Barthelemy said. "I'm completely focused on this fight against Relikh and making history, but I would be prepared to fight Mikey Garcia soon.

"Garcia versus Lipinets is going to be a great fight and I definitely want the winner. Although Lipinets is the underdog going into this fight, I think he's going to give Garcia all he can handle. But I still think Garcia will come out on top, setting up war between us in a unification bout."

First, Barthelemy has to contend with Relikh, a fight for which he said he has changed some of his training habits after last year's uneven performance.

"I'm going to change a lot heading into the rematch. Last May I wasn't myself," Barthelemy said. "I didn't feel like I had my legs coming into the fight and I wasn't able to perform how I usually do. This time my conditioning and nutrition is much improved. I'm going to use my legs and use my jab and put on a boxing clinic.

"Throughout my career I haven't paid enough attention to nutrition. It made my performances inconsistent. [Strength and conditioning coach] Bob Santos has come in and completely changed that. You'll see my conditioning on fight night is the best it's ever been. There was nothing surprising about Relikh in the first fight. We knew he'd have power, but unfortunately I had to change my game plan when my body wasn't cooperating. I traded shots and fought his fight. I'm going to stick to my plan this time."

Relikh (21-2, 19 KOs), 28, of Belarus, has lost two fights in a row, the hard-luck decision against Barthelemy and a unanimous decision in 2016 to Ricky Burns on Burns' home turf in Glasgow, Scotland, challenging for the same belt he will attempt to win against Barthelemy.

He also is determined to win the title and move on to a much bigger fight.

"First I have to win this fight," Relikh said. "But then I have hopes of a great year defending my belt against the mandatory and eventually a unification fight. This will be the year I reach a new level in this sport. I will have my eye on the main event for sure. I'm focused on Barthelemy now, but I want to unify and if that means fighting Garcia or Lipinets, I will be ready.

"This is my second time fighting for a world title and it will be a second lesson for me. This is my time to become champion. I need to do much more during this fight. I have to be aggressive right from the start. I'm sure that I need a knockout to get the victory. He can try to run, but he won't be able to hide from me."

Two additional undercard bouts will air on Showtime Extreme beginning at 8 p.m.: a lightweight world title eliminator pitting Richard Commey (25-2, 22 KOs), 30, of Ghana, against Alejandro Luna (22-0, 15 KOs), 26, of Bellflower, California, for the right to challenge for the world title currently held by Robert Easter Jr., and San Antonio junior welterweight prospect Mario Barrios (20-0, 12 KOs), 22, taking on Eudy Bernardo (23-2, 17 KOs), 31, of the Dominican Republic, in a 10-rounder.